Rubber-covered cylindrical rollers are widely used in industry for a number of applications, particularly for web or sheet handling and processing applications such as the embossing, calendering, laminating, printing and coating of paper, film, foil, and other materials. In addition to their use in web processing equipment, such rubber-covered rollers are often employed in conveyors and various office machines. Such rollers are typically comprised of a cylindrical (metal) core or other support with an outer covering of rubber, elastomer, or polymer material. However, after extended use, the covering on the rollers wears down and must be resurfaced or replaced. This typically requires that the rollers be sent to an outside source where the old surface is ground down and a new surface is applied. This is inconvenient and expensive as it requires that the processing equipment be shut down while the roller is being resurfaced or that the end user stock additional replacement rollers.
The printing industry uses a device called printing blankets to, for example, transfer ink from a device to a substrate, say paper. In one embodiment this is termed off-set printing. Rubber-covered cylindrical rollers are widely used in industry for a number of applications, particularly for web or sheet handling and processing applications such as the embossing, calendering, laminating, printing and coating of paper, film, foil, and other materials. In addition to their use in web processing equipment, such rubber-covered rollers are often employed in conveyors and various office machines. Such rollers are typically comprised of a cylindrical (metal) core or other support with an outer covering of rubber, elastomer, or polymer material. However, after extended use, the covering on the rollers wears down and must be resurfaced or replaced. This typically requires that the rollers be sent to an outside source where the old surface is ground down and a new surface is applied. This is inconvenient and expensive as it requires that the processing equipment be shut down while the roller is being resurfaced or that the end user stock additional replacement rollers.
Cylindrical rollers are widely used in the printing industry. For example, printing rollers or sleeves are used in the flexographic printing industry and in the offset printing industry for providing a mountable surface for flexographic printing plates or offset printing blankets. In a typical flexographic printing press, the sleeve is mounted onto a printing cylinder using pressurized air to expand the sleeve, and the printing plates are then attached to the outer surface of the sleeve. In an offset printing process, the blanket is mounted onto a printing cylinder using pressurized air to expand the blanket.
The prior art for preparing a compressible layer for a printing blanket, as discussed in U.S. Pat. No. 5,553,541, utilizes threads as a carrier for the rubber composition and the entrapped microcells. Microspheres from are available commercially from EXPANCEL Inc., an AKZO NOBEL Co., Duluth, Ga. USA. The thickness of the prior art compressible layer is by the number of threads wound and is determined by the coating of threads of different thicknesses. The threads act as a carrier for the compressible microcellular rubber formulation, and form a partially inelastic layer of different physical characteristics than the remaining portion of the layers in the blanket. The threads are wound under tension, and the deposited layer typically stratifies to a thread-rich inner portion and a thread-poor outer portion. The use of threads is expensive and time consuming. Additionally, we have found that the presence of threads close below the face layer of the printing blanket may cause print imperfections due to a variation in pressure points. The apex of the threads applies more pressure to the printed surface then the area where two threads meet and adjoin each other, and the inelastic nature of the threads appears to result in standing waves formed where a cylindrical printing blanket which a substantially inelastic layer, for example a thread layer, contacts the substrate.
While not used commercially, U.S. Pat. Nos. 5,323,702 and 5,553,541 describe applying a compressible layer by metering with a doctor roll, a doctor blade, or by conventional spraying. Applicants have found that conventional spraying results in 1) too thin a layer being deposited, such that many tens of layers must be sprayed to achieve the desired thickness, 2) too thick a layer is deposited, resulting in solvent inclusions that form rogue cells which impair blanket performance, or 3) both.
U.S. Pat. Nos. 4,430,406, 5,035,950, and 5,474,850, the disclosures of which are incorporated herein, describe spraying a coating on a cylindrical object to form a thin, even coating useful for a fuser member.
Printing blankets must follow every exact standards in terms of thickness, wettability, expandability when mounting, compressibility, an heat generation. The one test which incorporates one or more of those parameters is a test known as compliancy, which is known to those of skill in the art. Prior art blankets have a compliancy of between about 36 and 52, where the higher the number is the less a blanket is able to absorb an impact with multiple sheets of paper which may accidently be fed into the machine. The blanket thickness is generally in the range of 0.06 inches, and a paper may have a thickness of 0.007 inches. If multiple pieces of paper are drawn into a printer, the blanket is severely shocked, and the higher the compliancy value, the more of a shock is transmitted to the printer. Too low a compliancy, however, has been associated with poor print quality.
What is needed is a method of depositing a layer on a printing blanket assembly which does not result in commercially unacceptable rogue cells. What is also needed is a commercially acceptable method of manufacturing a printing blanket without threads or other substantially inelastic layer. Alternatively, what is needed is a commercially acceptable method of manufacturing a printing blanket without threads but with a thin substantially inelastic layer. What is also needed is a blanket with a lower compliancy that has acceptable print characteristics. The present invention in its many embodiments meets these needs.